During aircraft transition from en route to landing, air traffic controllers frequently issue instructions (or clearances) to change aircraft trajectories. These instructions can include temporary altitude assignments for level segments, speed adjustments, or lateral vectoring, enabling traffic controllers to manage air traffic flow while ensuring proper aircraft separation and flight safety. However, these controller instructions may also require aircraft to execute suboptimal tactical maneuvers, such as stair-step descents. A stair-step descent burns significantly more fuel and generates more carbon emission and engine noise than an uninterrupted Optimal Profile Descent (OPD) because OPDs use idle or near-idle thrust to execute a smooth speed-and-altitude profile during the descent phase of flight, while complying with multiple path constraints.
The drawback to OPDs is that, if only idle thrust is used during descent, the descent profile (i.e., the vertical path that aircraft flies) is a function of not only aircraft speed, aircraft weight, wind and temperature, but also aircraft platforms and engine types. Therefore, the idle descent profile can vary from one aircraft to another and from one flight to another flight at a different date. In other words, the vertical profile of OPD with idle thrust may not be repeated exactly by another aircraft or for another flight by the same aircraft. Therefore, how to incorporate OPDs with idle thrust into traffic flow without reducing air traffic capacity around an airport is a key operational consideration. One way to eliminate this concern of path unpredictability, while retaining most of OPD benefits, is to only use path segments with constant flight path angles during descent. Thus, the vertical descent profile is clearly defined. The difference in fuel savings between descent profiles with idle thrust and descent profiles with constant flight path angles are relatively small. But, the descent profile with constant flight path angles is predictable, even though it requires the use of near-idle thrust and speed brake.
Various OPD flight trials with different air-ground collaboration architectures have been conducted to evaluate the operational benefits and issues of OPDs. Depending on the air traffic density around the airport, the degree of interaction between air traffic controllers and pilots can vary greatly. For airports with light traffic environments, little interaction is needed to enable OPDs and OPDs can be performed most of the time, if aircraft is properly equipped. OPDs can currently be performed at a few select busy airports during off-peak hours.
To enable OPDs without reducing traffic capacity throughout the Terminal Radar Approach Control (TRACON) area, a Required Time of Arrival (RTA) constraint is usually imposed by air traffic controllers at a metering waypoint on the boundary of the TRACON area or on an Initial Approach Fix (IAF) to enable safe air traffic merging.
Consequently, it would be advantageous if an apparatus existed that is suitable for in-flight constructing a four dimensional trajectory for implementing an OPD to arrive at a metering waypoint at a RTA.